Reviewed-by <Anastasiia Lukianenko vicooodin@gmail.com>

Regards, Anastasiia

On Wed, Nov 15, 2023 at 2:53 AM AKASHI Takahiro takahiro.akashi@linaro.org wrote:

The current implementation may cause BUG_ON() in blkfront_aio() BUG_ON(n > BLKIF_MAX_SEGMENTS_PER_REQUEST);

In pvblock_iop(), a read/write operation will be split into smaller chunks of data so that the size in one access (aio_nbytes) is limited to, at the maximum, BLKIF_MAX_SEGMENTS_PER_REQUEST * PAGE_SIZE

But this works only if when the *buffer* passed in to pvblock_io() is page-aligned. If not, the given data region may stand across (BLKIF_MAX_SEGMENTS_PER_REQUEST + 1) pages. See the logic in blkfront_aio(): start = (uintptr_t)aiocbp->aio_buf & PAGE_MASK; end = ((uintptr_t)aiocbp->aio_buf + aiocbp->aio_nbytes + PAGE_SIZE - 1) & PAGE_MASK; Then this will lead to BUG_ON() above.

This can be fixed by decreasing the maximum size of aio_nbytes.

Signed-off-by: AKASHI Takahiro takahiro.akashi@linaro.org Fixes: commit 3a739cc6c948 ("xen: pvblock: Implement front-back protocol and do IO")

---

drivers/xen/pvblock.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/pvblock.c b/drivers/xen/pvblock.c index 4ad548d599d5..1df04e239ad0 100644 --- a/drivers/xen/pvblock.c +++ b/drivers/xen/pvblock.c @@ -632,7 +632,8 @@ static ulong pvblock_iop(struct udevice *udev, lbaint_t blknr, memcpy(blk_dev->bounce_buffer, buffer, desc->blksz);

            aiocb.aio_nbytes = unaligned ? desc->blksz :

•                   min((size_t)(BLKIF_MAX_SEGMENTS_PER_REQUEST *
  

PAGE_SIZE),

•                   min((size_t)((BLKIF_MAX_SEGMENTS_PER_REQUEST - 1)
  

•                                   * PAGE_SIZE),
                        (size_t)(blocks_todo * desc->blksz));
  
            blkfront_io(&aiocb, write);
  

-- 2.34.1